Preparation of chlorine and alkali metal nitrate as a side reaction in the production of nitric acid

ABSTRACT

A method for producing chlorine and alkali metal nitrate which comprises reacting nitrogen peroxide, water and oxygen in the presence of an aqueous nitric acid containing a nitrate of a group Ia metal having an atomic weight at least as heavy as potassium and reacting a chloride of alkali metal with the resulting solution.

O Unlted States Patent 1151 3,66l,5 1 2 Oushiba May 9, 1972 541PREPARATION OF CHLORINE AND UNITED STATES PATENTS ALKALI METAL NITRATEAS A SIDE 1,503,259 7/1924 Bergue ..23/160 REACTION IN THE PRODUCTION OF1,948,968 2/1934 Kramer et al. ..23/157 NITRIC ACID 3,211,525 10/1965Smith et al. ..23 15s x Inventor: Takashi Oushiba, y Japan 3,2 Beekhu1sl X 3,440,011 4/1967 Varlaeten et al. ..23/2l9 [73] Assignee: ShowaDenko Kabushiki Kaisha, Tokyo,

Japan Primary' E.\'an1inerOscar R. Vertiz [22] Filed: AP 23 1959Assistant Examiner-G O. Peters Attorney-George B. Oujevolk 21 Appl. No.:819,514

[57] ABSTRACT [30] Foreign Apphcauon Priority Data A method forproducing chlorine and alkali metal nitrate Apr. 26, 1968 Japan..43/27696 which comprises reacting nitrogen peroxide, water and oxygenin the presence of an aqueous nitric acid containing a [52] [1.8. Cl..23/l02, 23/161 nitrat ofa group 1a metal having an atomic weight atleast as Cold Colb 21/44 heavy as potassium and reacting a chloride ofalkali metal with of Search 219 the resulting olution,

References Cited 8 Claims, 2 Drawing Figures PATENTEUHAY 9 m2 SHEET 2[IF 2 -52: QZEQSE INVENTOR.

BY h y 1 PREPARATION OF CHLORINE AND ALKALI METAL. NITRATE AS A SIDEREACTION IN THE PRODUCTION OF NITRIC ACID This invention relates to newand useful improvements in preparing nitric acid containing dissolvedpotassium nitrate and particularly strong nitric acid solution. Theresultant strong nitric acid may be removed as the product, fractionatedup to 100 percent nitric acid or utilized in a process for react-. ingchlorides of potassium to produce potassium nitrate and nitrogendioxide, the latter being subjected to withdrawal, to fortify nitricacid in the system by means of my invention described later. Sincepotassium chloride is used as starting material for the production ofpotassium nitrate, at least a portion of the resultant potassium nitratemay be dissolved in said nitric acid during the process of preparing bymeans of this invention the concentrated nitric acid which is necessaryfor the above mentioned chloride reaction.

This invention also relates to a process wherein the starting chlorideis exposed to relatively high concentrations and excess stoichiometricquantities of HNO to maintain high concentrations of nitric acid in areacting and a stripping .zone under conditions permitting completestripping of chlorine and nitrogen dioxide produced, although strippingof chlorine is more important as its presence tends to reverse thedesired reaction that is, 3KCl 4 I lNO 3KNO NOCL' CL 214 0. A furtherimportant feature of this invention is that, in place of the weak nitricacid hitherto used as a starting material for the preparation ofpotassium nitrate and chlorine from potassium chloride, nitrogenperoxide is used.

Throughout this specification, the term strong nitric acid refers tonitric acid concentrations with water wherein the acid component isgreater than the normal azeotropic composition, i.e., from above about68 up to 100 percent l-lNO by weight. Weak nitric acid refers to anyacid concentration with water below the normal azeotropic composition,i.e., below about 68% l-INO; content. The concentrations for pur posesof measurement unless otherwise specified, refer only-to the nitric acidand water components and are not concerned with any other material,particularly not with nitrates, which may also be present in themixture. V

The term nitrogen peroxide" refers to nitrogen dioxideor nitrogentetroxide or a mixture of these. The term"nitrogen peroxide refer toalso the same containing nitrogen oxideand nitrogen trioxide.

As is well known, ordinary absorption of nitrogen dioxide will notproduce strong nitric acid. Strong nitric acid. is produced directly bythe reaction of liquid NO, (as N oxygen and water under a pressure, of50 kg/cm in an autoclave for about 4 hours.

It is also known that chlorine may be produced by reacting nitric acidand an alkali metal chloride to form the corresponding alkali metalnitrate and a gaseous mixture. of nitrosyl chloride and chlorine fromwhich the chlorine may be recovered by separation from the nitrosylchloride.

3 KC] 4 HNO;, 3 KNO NOCL CL 2 H O 3 HC] 4 HNO:, 3 HNO;, NOCl CL, 2 H O.

It has been recognized that the separate recovery of the nitrogen andchlorine combined as nitrosyl chloride is an important factor in theeconomic use of that process for the commercial production of chlorine.Accordingly, it has been proposed to decompose the nitrosyl chloride byany one of nu,- merous methods. Among such methods, it has been proposedto oxidize the nitrosyl chloride to nitrogen dioxide and chlorine byconcentrated nitric acid, and then separate the chlorine from thenitrogen dioxide.

The nitrogen dioxide formed is absorbed in water to form nitric acidwhich, by again being reacted with alkali metal chloride, serves toproduce additional nitrate and chlorine.

If it is desired to use strong l-lNO: for the oxidation of nitrosylchloride in the manner described above, this becomes an expensiveprocess, as conventional commerciall-lNO does not go above the normalazeotropic composition (68% HNO Therefore, it is an object ofthisinvention to prepare the strong nitric acid in a practical way.

It is also an object of this invention to utilize .nitrogenperoxide asstarting material.

It is likewise an object of this invention toestablish .conditionswherebythereaction of KC] with I-lNO to form KNO and/ C], may go readilyto completion so as to eliminate chloride in the early stages, as farasequipment is concerned, so that expensive corrosion-resistant equipmentis not necessary in the later stages of the process...

It is an additional object of this invention to optionally producestrong l-lNO within the chloride to chlorine process to be used in thebasic reaction.

It is another object of this inventionthat the chloride be substantiallycompletely reacted and then recovered as Cl,.

it. is also an object of this invention that all of the nitrogen fromthe used nitrogen peroxide" ultimately be removed with oxygen ,used, asKNO In connection with the fact that the nitrates of group la metalshaving an atomic weightat least as heavy as potassium,

when dissolved in an. aqueous solution of HNO shift the azeotropic pointupwardly for HNO; (downwardly for H O), I discovered thata concentratedsolution of HNO higher than 68 percent may be obtained at rather lowerpressure than in the old process described above by reacting nitrogenperoxide, oxygen and nitric acid in the presence of dissolved, excess N0and/or N 0 and potassium nitrate. having an atomic weight at least asheavy as potassium. Strong pure HNO may be obtained from the solutionobtained above by removingexcess NO, and/or N 0 by means ofvaporization, by removing nitrate mentioned above in solution bydistillation and by rectifying the liNO -H o vapor obtained.

The concentrated solution of HNO with or without thedissolved potassiumnitrate mentioned vabove may react with KC], NaCl, HCl or NOC] toproduce the corresponding nitrate, nitrogen dioxide and then .a part ofchlorine and the formed nitrate solution of aqueous nitricacid mayberecycled to produce more concentrated nitric acid by the processmentioned above.

For the proper understanding of my overall I chloride to chlorineprocess the following reactions are necessary:

2N0: N304 N204 20 02 KC] 4l-lNO 3KNO NOCl C], 211 0 .NOC] 2HNO 3N0, Cl HO KC] N0 1% 0 KNO Cl; Reaction 5 is the sum of reactions 1, 2, 3 X 1 and4X s.

Thus, I have developed an overall process culminating in reaction-5, andhave thus obtained the ultimatetheoretical af: fectiveness obtainable inconverting KC], NO, and 0,.to KNO, and C1 with the aid of nitric acidwith potassium nitrate that need notbe ultimately consumed. This nitricacid solution of potassium nitrate is necessary both as the solvent formaking higher super. azeotropic nitric acid and as the medium forintroducing solid potassium chloride to the chloride. reaction system inthe form of aslurry with strongnitric acid solution without theevolution of harmful gases, i.e., NOC]. Therefore, this solution is onlya useful medium which recycles through the whole system without beinginvolved in any reaction.

Especially if the reactions 3 and-4 by HNO solution. containingpotassium nitrate are connected with the reaction 1 and 2, the finalreaction 5 takes place totally within these reaction systems. Therefore,there is an attractive advantage. in that the dehydration process i.e.,the evaporating or concerttrating of the solution is not necessary inthissystem.

My invention distinctly difiers from the known process i.e., S,W.P.process (U.S, Pat. No. 3,211,525, Chemical Engineering 198-200 Nov. 8(1965)) in the fact; that in. the later the nitric acid has to beprepared by the knownprocess and concentrated so that the wateraccompanying the reactionsform; ing nitric acid is first-introduced fromthe outside of the system and is then has to be eliminated from thesystem after the reaction consuming nitric acid. In contrast to thelatter process, in my process the nitric acid necessary to the reaction3 and 4 may be easily prepared in the system according to myaforementioned process, so that the water necessary to form nitric acidcan be supplied from the system itself and recycled through the systemwithout entering or leaving it.

My invention also distinctly differs from the known process in the factthat in my process potassium chloride may be easily introduced into thesolution of potassium nitrate i.e., potassium nitrate in concentratednitric acid of 80 percent or greater HNO concentration at or below theordinary temperature and the formed slurry of the chloride in the nitricacid solution can be heated to the temperature suitable to considerablypromote the reaction 3 and 4 together. 7

l have found that it is more advantageous to react for a relativelyshort period of time the chlorides with the solution of the salt innitric acid in sufficient quantities and at proper temperature topromote reaction 3 and 4 without further aid.

Thereafter, however, the liquid resultants must be treated to strip theresulting gases from the liquids. Thus the resulting liquids areintroduced into a separation area where any chlorine containing gasesare completely eliminated.

The strong nitric acid is formed in the process by my invention whereinnitrogen peroxide, oxygen and water contained in weak, used nitric acidreact, in the presence of said weak, used nitric acid containing KNO,and excess N and/or N 0,, at or above the ordinary temperature and atordinary or greater than ordinary atmospheric pressure according to thereactions 1 and 2, to form nitric acid having a concentration of HNOgreater than the normal azeotropic composition. In these reactions, theN0 may be supplied partly from an outside source and partly from thechloride reaction zone according to the reaction 4 through a rectifier.It must be emphasized that my process does not require any nitric acidto be supplied from an outside source since my process itself contains aprocess for directly manufacturing strong nitric acid from nitrogenperoxide." The strong nitric acid of 80 percent or greater HNOconcentration by my invention can be used to react with potassiumaccording to the reactions 3 and 4 with or without the alkali metalnitrate. It is noted that the strong nitric acid, even though itcontains the nitrate necessary to my process, is so strong as toconsiderably promote oxidation of potassium chloride to potassiumnitrate and chlorine according to the reactions 3 and 4.

In practicing my invention, i.e., in the manufacture of chlorine anpotassium nitrate from the corresponding chlorides, it is advantageousto divide the reaction system into two or more reactions systems becauseof the difference of the conditions of the individual reactions, thoughit is possible to force them into one reaction system.

The first reaction system is that for preparing nitric acid according tomy invention described above in which in the presence of nitric acid,the concentration of which is at least 50 percent, of potassium nitrateand of liquid nitrogen peroxide," oxygen or oxygen containing gases andwater which is contained in the nitric acid react to form HNO thusultimate- I ly raising the concentration of HNO of the original weakaqueous nitric acid.

The temperature of the system is in the range of from ordinarytemperature to the boiling point of the liquid though I recommend theuse of temperatures between 30 C. and 70 C. according to the content ofnitrogen peroxide in the liquid and the pressure of the system. Thehigher the temperature of the system, the higher the rate of thereaction.

The pressure of the system is in the range of from ordinary atmosphericpressure to about 100 times atmospheric pressure though I recommend theuse of pressures between ordinary atmospheric pressure and about timesatmospheric pressure. The higher the pressure of the reaction system,the higher the rate of the reaction. The higher the concentration ofpotassium nitrate and nitrogen peroxide in the liquid in the system, thehigher the rate of the reaction to form nitric acid, but it isadvantageous to use a concentration of potassium nitrate up to the halfof saturation and a concentration of nitrogen peroxide" in the range of5 to 30 percent.

It is more advantageous to recycle unreacted NO,, 0,, NO etc. in theprocess of preparing nitric acid into the first raw gases or repeat thereaction in several steps in the packed tower, for example to react themeffectively. In this process nitrogen oxide NO and nitrogen trioxideN,O, formed can be oxidized both in the gaseous phase and in thenitrate-nitric acid solution. Accordingly it is fully possible to useNO, which contains some NO.

For the purpose of manufacturing strong nitric acid, one can treat thesolution of potassium nitrate in concentrated nitric acid prepared inthe manner hereinbefore described to first remove excess N0 from thesolution, to then evaporate HNO -I-I O vapor from the solution toseparate the potassium nitrate and finally to rectify I-INO --H,O vaporto obtain 99% l-lNO For the purpose of preparing chlorine, potassiumnitrate and N0 from alkali metal chloride using HNO; containing H O, oneneed not treat the aforementioned nitrate-nitric acid solution toseparate 99% HNO but may utilize the former solution directly for thereaction with the chloride.

The second reaction system is thus, that of reacting potassium chloride,with I-INO In this system, nitric acid used may be either clean and saltfree or it may contain nitrate. It it is preferable to remove free N0and/or N 0 from these HNO, aqueous solutions because these componentsreact easily with the chloride even at low temperature to form harmfulgases, i.e., NOCl and potassium nitrate and thus make it difficult tointroduce the chloride into the system.

In this reaction system the reactions 3 and 4 proceed in one or morereaction units. It is preferable to make the chlorine stripping unit apart of this reaction system in order to completely remove all chloridein processing the solution from this point on so as to eliminate theproblem of corrosion that is normally encountered in the admixture ofthe chlorides with I-IN O The higher the temperature of this secondsystem, the faster the rate of the reactions 3 and 4. The pressure ofthe system need not be much higher than atmospheric pressure.

The rates of the reactions 3 and 4 are considerably high if the finalconcentration of I-INO; is more than 70 percent and the temperature ofthe reaction is as high as about 100 C.

From the second reaction system, the liquid products are cooled tocrystallize potassium nitrate and separate it by an appropriate way fromthe motor liquor which contains potassium nitrate in aqueous nitricacid. This mother liquor is recycled to the first reaction system formanufacturing HNO The gaseous reaction products from the second reactorcomposed of Cl:, NO CI, NOCl, NO, N0 and HNO are cooled to reflux someof the N 0 and the greater part of the I-INO at materially 100 percentconcentration. This l-INQ has the ability of oxidizing more NOCl. Theremaining gases are carried to the following separation system.

The third system is for separation of pure C1 and pure N 0 These gaseousmixtures are rectified by the known methods. Liquid chlorine is one ofthe main products by the process by my discovery. On the other hand theliquid N 0 can be used as the source material for the first reactionsystem for HNO by my process.

In practicing this process nitryl chloride forms and builds up in therecycle gas stream of the total reaction systems to a steady-state valuethat is limited by thermodynamic equillibria.

Consequently the merits of this invention are as follows:

At first, strong nitric acid of concentration as high as 70 to 100percent HNO is directly manufactured from nitrogen peroxide", oxygen oroxygen containing gases and H 0 at considerably lower temperature andlower pressure in my process than ordinary methods.

Secondly, in manufacturing chlorine and potassium nitrate from thecorresponding chloride, nitrogen peroxide and oxygen in my process,there forms no H O, whereas water always forms in ordinary processes,and therefore my process necessitates neither dehydration norconcentration.

Thirdly, as nitric acid is not the source material for this process,preliminary production of dilute nitric acid is not necessary. The onlysource materials for my process are the nitrogen peroxide" prepared byoxidation of NO which is prepared from the oxidation of NR Therefore thetotal process for my invention is'exceedingly simple compared with anyone other processes hitherto carried out.

With the above objects and features in view, the nature of which will bemore apparent, the invention will be more fully understood by referenceto the drawings, the accompanying detailed description with examples andthe appended claims. In the drawing:

FIG. 1 is a flow-sheet illustrating an embodiment for efiecting thereaction of the aqueous nitric acid containing potassium nitrate whichis produced according to the method of this invention.

FIG. 2 is a flow-sheet illustrating an embodiment for producing nitricacid according to the method of this invention.

Referring to the drawings, especially to FIG. 1, 1 is an apparatus forproducing nitric acid into which aqueous nitric acid containingpotassium nitrate and nitrogen peroxide has been introduced. A mixtureof pure oxygen and gaseous N is introduced into said apparatus 1 in theform of fine bubbles while said aqueous nitric acid is stirred, and themixture is reacted with said solution.

The aqueous nitric acid so obtained is heated at 80 C. In bleachingtower 2 to evaporate nitrogen tetroxide. The nitrogen tetroxideevaporated is recycled to apparatus 1 for producing nitric acid. Theaqueous nitric acid containing potassium nitrate remaining in thebleaching tower 2 is carried to mixer 3 to mix with potassium chloridechloride. The mixture thus obtained is introduced into main reactor 4which is maintained at normal atmospheric pressure at about 90 C. to 140C. Gases generated in main reactor 4 such as NOCl, N0 N0 Cl, C1 N 0 HNOH O, etc. according to the raw materials used, are sent together withthe liquid produced in the reaction to gas-liquid separator 5 connectedat its top to reflux condenser 6 which is maintained at 5 C. to C. Ofthe gases mixed with the liquid, the total amount of the I-INO and the H0 and a part of the N0 are condensed by the means of reflux condenser 6and flow back to gas-liquid separator 5.

The gases which have passed through reflux condenser 6 are, after beingcooled to 10 C. to 5 C. in cooler 7, carried to chlorine rectifier 8,and 99.5 percent of liquid chlorine is obtained at the top of saidrectifier 8.

The remaining solution in chlorine rectifier 8 is introduced into N 0rectifier 9. The volatiles constituents more volatile than N 0,, aretaken from the top of said rectifier 9 and recycled to main reactor 4.Further, the 99.5 percent N 0 solution obtained from the bottom of N 0,,rectifier 9 is returned to apparatus 1.

The aqueous nitric acid containing potassium nitrate obtained by gasliquid separator 5 is carried to separator 10 to vaporize a small amountof chlorides, the vapor being recycled to gas-liquid separatorS. Theremaining solution is cooled to about C. in crystallizer 11 wherein thepotassium nitrate precipitates as crystal. The crystal obtained is sentto separator 12, and the residue is recycled to apparatus 1.

Furthermore, when a reaction system for producing strong nitric acid asshown in dotted lines is provided in addition to the reaction systemdescribed above, strong nitric acid, chlorine, and nitrate can beinstantaneously produced with one reaction system.

Referring to FIG. 2, NO, NO,, N 0 and O, are introduced into apparatus 1for producing nitric acid as raw materials in the same way as in FIG. 1.The aqueous nitric acid obtained is heated in bleaching tower 2 tovaporize nitrogen tetroxide, and the vaporized nitrogen tetroxide isrecycled to apparatus 1 for producing nitric acid. The remaining aqueousnitric acid containing potassium nitrate in bleaching tower 2 isintroduced into evaporator 13 to generate nitric acid vapors from theaqueous nitric acid, and said vapors are introduced into rectifier 14after being cooled, to obtain a strong nitric acid of high purity. Theremaining aqueous nitric acid in rectifier 14 and evaporator 13 isrecycled to apparatus 1 for producing nitric acid through line 15 whilesupplying water.

As mentioned above, the process by which this invention is carried outis very simple and more economical than that of the conventional arts.

The following examples are further illustrative of this invention, andit will be understood that the invention is not limited thereto.

EXAMPLE 1 Aqueous nitric acid (HNO KNO H O 56 21 23) prepared byresolving potassium nitrate and liquid nitrogen tetroxide correspondingto 25 percent of said solution by weight were previously introduced intoapparatus 1 for producing nitric acid in the flow-sheet as shown inFIG. 1. Then, a mixed gas of 1.4 m of pure oxygen and 5.5 kg of gaseousN0 per hour respectively was introduced into said apparatus at thepressure of 3 kg/cm at 50 C. so as to form fine bubbles while saidsolution and liquid were being stirred.

The mixed solution containing 221 kg per hour of aqueous nitric acid(I-lNO 2 KNO H 0 68 l5 l7) and liquid nitrogen tetroxide correspondingto 20% parts to 100 parts of the aqueous nitric acid by weight wasintroduced into bleaching tower 2 from said apparatus 1 and then heatedto C. Nitrogen tetroxide thus evaporated was recycled to saidapparatus 1. The remaining aqueous nitric acid was introduced into mixer3 to mix it with potassium chloride supplied at 9 kg per hour, and thencarried to main reactor 4 which was maintained at normal atmosphericpressure at l00 C. The gases generated by the reaction in reactor 4 wererefluxed and condensed, then cooled and carried to the chlorinerectifier. Thus, 4.2 kg per hour of 99.5 percent liquid chlorine wasobtained in the chlorine rectifier 8. The nitric acid containing nitrateseparated by gas-liquid separator 5 was cooled to 20 C. in crystallizer11. Thus, 12 kg per hour of potassium nitrate (purity 99.0 percent) wasobtained.

EXAMPLE 2 A mixed gas containing 1 1 kg of NO, 57 kgof N0 and N 0 10 kgof H 0, 16 m of oxygen and 80 m of nitrogen per hour respectively wasintroduced into apparatus 1 as shown in FIG. 2 at the pressure of 10kg/cm at 30 C. A solution of potassium nitrate in aqueous nitric acidrecycled from the following process into the top of the tower and wasallowed to flow down in counter current to the said mixed gases. Thesolution withdrawn from the bottom of the apparatus 1 was introducedinto a beaching tower 2 to remove nitrogen tetroxide which was recycledto the apparatus 1 and the remaining nitric acid solution of potassiumnitrate was next subjected vto vaporization to separate the mixed vaporsof I-lNO and H 0 at vaporizer 13. The nitric acid vapor was then carriedto a rectifier 14 and kg per hour of 99.9 percent pure l-lNO wasobtained from the top of said rectifier 14 and 68 percent pure HNOaqueous solution was obtained at the bottom of said rectifier 14. Boththe remaining solution at the vaporizer l3 and the residue at therectifier 14 were recycled to the apparatus 1 through line 15 whilesupplying 6 kg per hour of water.

By this reaction the concentration of aqueous nitric acid raised to 87.6percent that is 30 kg of I-INO was formed.

I claim:

l. A method of producing chlorine and potassium nitrate comprising thesteps of:

l. reacting excess nitrogen peroxide and oxygen with nitric acidcontaining at least 50 percent by weight of potassium nitrate to form ahigher super azeotropic nitric acid,

2. reacting at least a portion of said super azeotropic nitric acidcontaining potassium nitrate with potassium chloride to form additionalpotassium nitrate and gas containing chlorine and nitrogen peroxide,

3. separating said gas from said nitric acid solution containingpotassium nitrate, and

4. separating said gas into chlorine and nitrogen perioxide andrecycling said nitrogen peroxide to step l.

2. The process of claim 1 wherein a portion of said potassium nitrate isseparated from said nitric acid solution produced in step 2 and thenitric acid solution is recycled to step i.

3. The process of claim 1 wherein said step i is conducted at atemperature between room temperature and the boiling point of themixture.

4. The process of claim 1 wherein said step 1 is conducted at atemperature between 30 and 70 C.

5. The process of claim 1 wherein said step 1 is conducted at a pressureof from atmospheric to atmospheres.

6. The process of claim 1 wherein said step '1 is conducted at apressure of from atmospheric to 10 atmospheres.

7. The process of claim 1 wherein said super azeotropic nitric acidcontains at least 70 percent by weight of nitric acid.

8. The process of claim 1 wherein said step 2 is conducted at atemperature between room temperature and about 100 C.

2. The process of claim 1 wherein a portion of said potassium nitrate isseparated from said nitric acid solution produced in step 2 and thenitric acid solution is recycled to step
 1. 2. reacting at least aportion of said super azeotropic nitric acid containing potassiumnitrate with potassium chloride to form additional potassium nitrate andgas containing chlorine and nitrogen peroxide,
 3. separating said gasfrom said nitric acid solution containing potassium nitrate, and
 3. Theprocess of claim 1 wherein said step 1 is conducted at a temperaturebetween room temperature and the boiling point of the mixture.
 4. Theprocess of claim 1 wherein said step 1 is conducted at a temperaturebetween 30* and 70* C.
 4. separating said gas into chlorine and nitrogenperioxide and recycling said nitrogen peroxide to step
 1. 5. The processof claim 1 wherein said step 1 is conducted at a pressure of fromatmospheric to 100 atmospheres.
 6. The process of claim 1 wherein saidstep 1 is conducted at a pressure of from atmospheric to 10 atmospheres.7. The process of claim 1 wherein said super azeotropic nitric acidcontains at least 70 percent by weight of nitric acid.
 8. The process ofclaim 1 wherein said step 2 is conducted at a temperature between roomtemperature and about 100* C.